Techniques for image measurement of agricultural land are publicly known (for example, refer to Japanese Unexamined Patent Application Laid-Open No. 2014-089160). These techniques perform aerial photographing of agricultural land using an aircraft. The image measurement using aerial photographs requires ortho correction. To perform the ortho correction, data of parts that are easily recognizable in the aerial photographs (for example, curbs or white lines on roads, or manholes) or location data of targets, is necessary.